Experimental Investigation Of Plasma Characteristics In 13.56 MHz/2 MHz Cylindrical Inductively Coupled Plasma

In recent years,inductively coupled plasmas are widely used in semiconductor and display processes because of their desirable characteristics such as high plasma density,independently controllable ion energy and without electrode interference.As the chip area becomes larger and the etch line width becomes finer,which puts higher requirements on the plasma technology.The improvement of these process requirements is not only a technical issue,but also some complex physical problems involved in the plasma process.The generation and maintenance of plasma in the RF inductively coupled plasma sources are mainly realized by the time-varying electromagnetic field induced by the RF current.The electrons are accelerated inelastic collision with neutral particle by the electromagnetic.Therefore,the driving frequency is an important parameter for generating and maintaining the plasma,and is closely related to the performance of the plasma source.However,the effects of different driving frequencies on the radial distribution of the plasma parameters are hardly investigated.Hence,a large area cylindrical inductively coupled plasma source driven separately by 13.56 MHz(high-frequency)and 2MHz(low-frequency)is investigated.Firstly,the Langmuir double probe is used to measure the electron density and electron temperature at various powers and gas pressures at the high-frequency and low-frequency driving discharge,respectively.It is found that the effects of input power on plasma parameters at high-frequency and low-frequency are different.When discharge is driven at high frequency,the electron density increases obviously with the increase of power.However,when discharge is driven at low frequency,the electron temperature increases evidently with the increase of power.Secondly,the radial resolved measurements of electron density and electron temperature are systematically analyzed by means of Langmuir double probe at various powers and gas pressures.At a gas pressure of 10 Pa,the electron density shows a ‘convex' distribution and increases with the increase of input power for both the high-frequency and low-frequency discharge.However,the distributions of electron temperature at high-frequency and low-frequency are obviously different as the increase of input power.When the discharge is driven at high-frequency,the electron temperature is relatively flat in the center of the chamber and slightly increases on the edge.When the discharge is driven at low-frequency,the electron temperature gradually decreases along the radial position.At a gas pressure of 100 Pa,the electron density increases and then decreases with the increase of radial distance.The distribution shows a ‘saddle' shape for high-frequency and also for low-frequency discharge.Although the uniformity of electron density improves with the gas pressure,the uniformity at low-frequency is better than that at high-frequency.Finally,in order to further study the high-frequency and low-frequency discharge,and the difference of electron density and electron temperature with the parameters.Under the same conditions as the Langmuir dual probe measurement,the emission spectrum of argon plasma is collected by optical emission spectroscopy.The number density of the metastable states particles are calculated by the branch ratio method.It is found that the radial distribution of the electron temperature is always opposite to the radial distribution of the metastable particles.